You might be projecting your own reference frame on others a bit to much. "Please don't snipe" isn't overly descriptive for casual players who has no idea what is going on with the content. They see something pop up and might want to have a look what is going on. That casual player might just think: "I am not sniping anything... whatever that means. I'm just having a look what this thing is about. By all means go ahead, I wont bother you." If you want to organize group runs in the current environment and mechanics. It's your own responsibility to clearly communicate, at the very least.
And even when communicated clearly, it's against the TOS for tanks to intentionally kill other players with TB's. "I told them not to queue up" is not a valid defense.